CAB39 is a calcium-binding scaffold protein that stabilizes and activates the serine-threonine kinase STK11/LKB1, serving as a critical hub in cellular signaling networks. The protein facilitates kinase complex assembly and enhances the activity of downstream effectors including WNK kinases, SPAK, and OSR1, with studies showing CAB39 can enhance SPAK activity up to 100-fold 1. Through these interactions, CAB39 regulates ion transporters such as the sodium-chloride cotransporter (NCC) and sodium-potassium-chloride cotransporters, contributing to electrolyte balance and blood pressure control 1. CAB39 plays multifaceted roles in disease contexts. In bladder cancer, CAB39 overexpression promotes epithelial-mesenchymal transition and metastasis via NF-κB signaling activation, with CAB39 knockdown reversing invasive and metastatic behaviors in xenograft models 2. In cisplatin-resistant bladder cancer, CAB39 enhances survival through the LKB1-AMPK-LC3 autophagy pathway, maintaining mitochondrial health and reducing reactive oxygen species 3. Similarly, miR-451-mediated suppression of CAB39 drives chemoresistance in colorectal and pancreatic cancers via the AMPK-mTOR pathway 4, 5, and in diabetic cardiomyopathy, elevated miR-451 downregulates CAB39, exacerbating lipotoxic injury 6. Conversely, CAB39 upregulation through miR-107 inhibition activates AMPK-Nrf2 signaling to protect osteoblasts from dexamethasone-induced oxidative damage 7. These context-dependent roles suggest CAB39 inhibition as a potential therapeutic strategy for chemoresistant cancers 1, while CAB39 restoration may benefit metabolic and bone disease.